Wars of the Three Kingdoms: After crossing the Firth of Forth, English Commonwealth forces defeated a Scottish army at the Battle of Inverkeithing, opening the rest of the country to occupation.

The Wars of the Three Kingdoms were a series of conflicts fought between 1639 and 1653 in the kingdoms of England, Scotland and Ireland, then separate entities in a personal union under Charles I. They include the 1639 to 1640 Bishops' Wars, the First and Second English Civil Wars, the Irish Confederate Wars, the Cromwellian conquest of Ireland and the Anglo-Scottish War of 1650–1652. They resulted in the execution of Charles I, the abolition of monarchy, and founding of the Commonwealth of England, a unitary state which controlled the British Isles until the Stuart Restoration in 1660.

The Firth of Forth is a firth in Scotland, an inlet of the North Sea that separates Fife to its north and Lothian to its south. Farther inland, it becomes the estuary of the River Forth and several other rivers.

The Commonwealth of England was the political structure during the period from 1649 to 1660 when the Kingdom of England, later along with Ireland and Scotland, were governed as a republic after the end of the Second English Civil War and the trial and execution of Charles I. The republic's existence was declared through "An Act declaring England to be a Commonwealth", adopted by the Rump Parliament on 19 May 1649. Power in the early Commonwealth was vested primarily in the Parliament and a Council of State. During the period, fighting continued, particularly in Ireland and Scotland, between the parliamentary forces and those opposed to them, in the Cromwellian conquest of Ireland and the Anglo-Scottish war of 1650–1652.

The Battle of Inverkeithing was fought on 20 July 1651 between an English army under John Lambert and a Scottish army led by James Holborne as part of an English invasion of Scotland. The battle was fought near the isthmus of the Ferry Peninsula, to the south of Inverkeithing, after which it is named.